The act of being a total wuss who can't take their booze.
You can spot a 'Cupper' at any party as they are the ones lifting the booze to their lips but failing to actually sup it!!!!
Barbara - "see Brian over there???...... you want to know why he's still standing?????"
Jesus - "Why...... I'm mashed, I've been sick in my hair and can barely see straight and we arrived at the same time?"
Barbara - "Cupping it..... not supping it!"
Jesus - "What do you mean Barbara?"
Barbara - "Watch him.... he's cupping his booze.... but when he raises it to his lips, the fooker fails to sup it.
Jesus - "Bugger me, he's a Cupper not a Supper!!!"